Add session-app RBAC element type for session app access control

== Motivation ==

Admins should be able to access compute session listings and detail panels, but session app access must be controlled by a separate permission. The current RBAC element type cannot separate session metadata access from app access.

== Objective ==

Add a session-app value to the RBAC element type, so that session app access permission can be managed separately from session metadata access.

== Expected Sub Issues ==

1. Add session-app to RBAC element type enum

2. Apply RBAC creator pattern for session-app

3. Data migration for session-app RBAC element type

JIRA Issue: BA-5376